Job stress may have been behind a threatening email and potential gun violence that the Jacksonville Sheriff's Office says appears to have been thwarted by a police-involved shooting Tuesday. That's the theory of an anonymous co-worker of 51-year-old Tammy Gill.

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Gill is in jail and charged with carrying a concealed weapon, making written threats and fleeing police.

According to investigators, Gill was driving a pickup truck in East Arlington Tuesday and fleeing from a disturbance at a sporting goods store when her passenger, 56-year-old Lesley Cowan, fired at officers who fired back, killing him.

On Tuesday, the Sheriff's Office said the two may have been preparing a revenge-fueled killing against the owners of Atlantic Self Storage on Mayport Road, where Gill was a manager who lived on the property.

In an interview with Channel 4 Wednesday night, one of Gill's co-workers said she suspects that a stressful work environment contributed to whatever was going on with Gill and her boyfriend.

Her co-worker wanted to remain anonymous for fear of losing their job.

"I just know the managers are hard-working people," said Gill's co-worker. "And they're under a lot of stress to get their numbers up or they will have to vacate the property in three days of the day they get fired. If they fire, you have to move out because you're a resident manager."

The co-worker showed Channel 4 an email from the company saying that their employees were not allowed to speak to the media about Gill's case.

Police said Gill was being terminated from her job. According to investigators, about 30 minutes before the incident with police, Gill sent an email saying she intended to kill the company's owner, his family and "anyone who stood in their way."

The employee said they don't believe a stressful work environment justifies Gill's actions, but hopes these events can lead to changes in morale at the company.